In the physical topology design, the number of OXCs and/or links is takes as the objective. In this paper, we take aim at minimizing the maximal optical port number of each OXC, given the number of OXCs and the traffic. We present a traffic-oriented heuristic algorithm to generate an initial topology. This presented algorithm outperforms the previous algorithm, since our presented algorithm takes into account the traffic pattern. Furthermore, we present a routing strategy that is a balance between the shortest-path routing and the least-congestion routing. The tabu algorithm is adopted to attain the optimal solution. We choose the path-based sharing protection scheme to provide 100% recovery guarantee. Numerical results demonstrate the effectiveness of our algorithm and strategy.
In this paper we consider the problem of designing a network of optical cross-connects(OXCs) to provide end-to-end lightpath services to label switched routers (LSRs). Like some previous work, we select the number of OXCs as our objective. Compared with the previous studies, we take into account the fault-tolerant characteristic of logical topology. First of all, using a Prufer number randomly generated, we generate a tree. By adding some edges to the tree, we can obtain a physical topology which consists of a certain number of OXCs and fiber links connecting OXCs. It is notable that we for the first time limit the number of layers of the tree produced according to the method mentioned above. Then we design the logical topologies based on the physical topologies mentioned above. In principle, we will select the shortest path in addition to some consideration on the load balancing of links and the limitation owing to the SRLG. Notably, we implement the routing algorithm for the nodes in increasing order of the degree of the nodes. With regarding to the problem of the wavelength assignment, we adopt the heuristic algorithm of the graph coloring commonly used. It is clear our problem is computationally intractable especially when the scale of the network is large. We adopt the taboo search algorithm to find the near optimal solution to our objective. We present numerical results for up to 1000 LSRs and for a wide range of system parameters such as the number of wavelengths supported by each fiber link and traffic. The results indicate that it is possible to build large-scale optical networks with rich connectivity in a cost-effective manner, using relatively few but properly dimensioned OXCs.
In this paper we consider the problem of reconfiguration of virtual topology on wavelength-routed optical ring networks with dynamic changes in traffic. Unlike previous studies on this problem, we select the traffic needing rerouting and the most congested link load as our objectives. In addition, we consider the traffic with both rapid and slow changes. When the traffic changes slowly, we will select the routing strategy based on the shortest path, taking into account the cost caused by the reconfiguration and choose a heuristic similar to generalized least processing time (GLPT) as the wavelength assignment algorithm. Our consideration does make sense in that the strategies mentioned above enable the virtual topology to be updated to follow the change in traffic closely, while considering some certain cost of the reconfiguration. On the other hand, if the traffic changes dramatically, we choose the strategy of adding lightpaths or deleting lightpaths(LAD). It is clear that this strategy will result in a smaller change in the virtual topology. This implies the reconfiguration will lead to a lower cost.
Numerical results show that our approach outperforms the previous ones and that we can set up a network with no change in our physical topology, which can sustain various patterns of traffic.
To cater for the burst characteristic of IP traffic, WDM networks are expected to reconfigure the virtual topologies corresponding to the real-time changes of the traffic flow. This paper introduces the elementary algorithms of the virtual topology reconfiguration. Compared to each other, we point out their advantages and disadvantages. Then our paper focuses on the tradeoff between the benefits and costs brought by the reconfiguration of the virtual topologies. We present a evaluation function and two thresholds, namely a lower and a higher. Our presented approach balances between the benefits and costs due to the reconfiguration of the virtual topology, increasing the benefits as much as possible while guaranteeing the low costs, with a distinguished characteristic of taking the state of the network into consideration.
In this paper we investigate the fairness problem of offset-time-based quality of service (QoS) scheme proposed by Qiao and Dixit in optical burst switching (OBS) networks. In the proposed schemes, QoS relies on the fact that the requests for reservation further into the future, but for practical, benchmark offset-time of data bursts at the intermediate nodes is not equal to each other. Here, a new offset-time-based QoS scheme is introduced, where data bursts are classified according to their offset-time and isolated in the wavelength domain or time domain to achieve the parallel reservation. Through simulation, it is found that this scheme achieves fairness among data bursts with different priority.
As a new solution of all optical networks, Optical burst switching (OBS) has been wildly studied in recently years for its high traffic throughput and high resource utilization at current technology level. In this paper we address some issues of efficient contention resolution: burst segmentation and deflection routing. Under the Just-Enough-Time (JET) protocol based OBS networks architecture, control packet is the guider for corresponding data burst during the transmission. Taking these into consideration, here we propose a novel segmentation strategy - current burst segmentation (CBS) and a modified deflection routing strategy fit for JET based OBSN. Through analysis and simulation, it is shown that these new strategies perform well.
A novel multistage optical cross-connect (OXC) that combined the advantages of three technologies of Space Division Switching (SDS), Wavelength Division Switching (WDS), and Optical Time-Division Multiplexing (OTDM) has been proposed. The structures of the first and second stages of a 2 X 2 and a 4 X 4 OXC have been presented. By means of the splitter and delivery (SAD) switch, it is cost-effective and fully modularized and very convenient to scale to n X n OXCs suitable for large-scale backbones.
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